1. Field of the Invention
The present invention relates to a formation method of a two-dimensional code by means of laser burning.
2. Description of the Prior Art
Generally, bar codes composed of printed stripes are used on packages of goods for merchandise control and accounting at a point of sales. Nevertheless, this bar code composed of stripes has a small amount of data to be recorded in comparison with an area to be used, and hence can be used only for control of article numbers of goods and the like.
For this reason, recently, a two-dimensional code that is formed by a matrix having a bright and dark dotted pattern has been used. Since this code can record 12 alphanumeric characters per 1 mm square, the data amount per unit area is extremely large in comparison with that of the bar code. Therefore, this code has such advantages that the code can not only record plenty of data but also read the data from any direction, that is, the direction of 360.degree. with a reader. Furthermore, since this code not only has a function of recovering data even if a part of the code is damaged or stained, but also can secretly manage information by encrypting data, its application has been widespread.
When this two-dimensional code is generated, image data composed of a matrix having a bright and dark pattern is generated on a screen of a personal computer with using a graphic software. Conventionally, a two-dimensional code is formed on a marking surface with a method such as presswork, printing with a printer, and laser burning on the basis of a two-dimensional code generated from this image data.
A two-dimensional code 1, as shown in FIG. 8, records data by forming a plurality of cells 2 through dividing an inside of a square or a rectangular into a matrix, and arraying cells 2a, which are derived from cells 2 and are darkly filled, and bright cells 2b. For example, if 25 pieces of square cells 2 are formed by dividing a two-dimensional code 1, having an area of 1.2 mm square, into squares with 5 rows and 5 columns, each cell 2 is formed in the shape of a square each side of which is 240 .mu.m long.
When a cell 2a, which is darkly filled, is formed on a marking surface of metal, resin, or the like with heat of a laser beam by irradiating the laser beam on the marking surface, first, as shown in FIG. 9A, a cell 2 is linearly burnt with the laser beam sequentially from an upper portion to a lower portion with making the laser beam horizontally scan. Finally, as shown in FIG. 9B, the dark cell 2a is formed by burning the marking surface in a square totally.
In this system, since there is no regularity in radiation intervals of a laser, the laser beam may be irradiated out of a cell area, and hence, for example, as shown in FIG. 10, runover portions 3, caused by the laser beam deviating horizontally, and a blank portion 4 may arise in some cases. If a two-dimensional code 1 including such irregular cells 2a is formed on a marking surface as shown in FIG. 11, this causes a problem that the code may be read as erroneous data by a reader. In particular, in case of a minute two-dimensional code with only an area of 1 mm square, read errors increase, and hence this causes a problem that an advantage of the two-dimensional code which can record plenty of information is extinguished.
This is because it is not defined in a conventional system that vector data necessary for forming a cell exists only in a cell area. Thus, the conventional system does not recognize each of 25 cells, formed in a matrix with 5 rows and 5 columns, as a unit cell, but generates the two-dimensional code by sequentially combining line-drawing continuous data in bit-map data on the basis of image data. Therefore, a coordinate management system of recognizing a starting point and an end point of marking is not adopted, and hence this causes a problem that irregular cells are formed.